Method and apparatus for the continuous production of silicon oxide powder

ABSTRACT

A silicon oxide powder can be continuously prepared by feeding a raw material powder mixture containing silicon dioxide powder into a reaction chamber ( 2 ) at a temperature of 1,100-1,600° C., to produce a silicon oxide gas, transferring the silicon oxide gas to a deposition chamber ( 11 ) through a transfer conduit ( 10 ) maintained at a temperature of from higher than 1,000° C. to 1,300° C., causing silicon oxide to deposit on a substrate ( 13 ) which is disposed and cooled in the deposition chamber, scraping the silicon oxide deposit, and recovering the deposit in a recovery chamber ( 18 ). The method and apparatus is capable of continuous and stable production of amorphous silicon oxide powder of high purity.

[0001] This invention relates to a method and apparatus for thecontinuous production of silicon oxide powder.

BACKGROUND OF THE INVENTION

[0002] In the prior art, silicon oxide powder is produced, as disclosedin JP-A 63-103815, by heat treating a raw material mixture containingsilicon dioxide base oxide powder in a reduced pressure, non-oxidizingatmosphere to generate SiO vapor, and condensing the SiO vapor in a gasphase, thereby continuously forming fine amorphous SiO particles with asize of 0.1 μm or less. Alternatively, silicon raw material is heated,evaporated and deposited on a surface of a substrate having a coarsestructure as disclosed in JP-A 9-110412.

[0003] The method of JP-A 63-103815 is capable of continuous production,but fails to produce high purity silicon oxide powder because the SiOpowder produced is a fine powder which undergoes oxidization when takenout in the air. The method of JP-A 9-110412 can produce high puritysilicon oxide powder, but does not lend itself to mass-scale productionsince it is of batchwise design. As a consequence, the silicon oxidepowder becomes expensive.

SUMMARY OF THE INVENTION

[0004] An object of the invention is to provide a method and apparatusfor the continuous and effective production of high purity silicon oxidepowder at a low cost.

[0005] It has been found that a silicon oxide powder can be continuouslyprepared by feeding a raw material powder mixture containing at leastsilicon dioxide powder into a reaction furnace heated at a temperatureof 1,100 to 1,600° C., to produce a silicon oxide vapor, transferringthe silicon oxide vapor to a deposition chamber through a transferconduit maintained at a temperature of from higher than 1,000° C. to1,300° C., causing silicon oxide to deposit on a surface of a substratewhich is disposed and cooled in the deposition chamber, scraping thesilicon oxide deposit at desired intervals, and recovering the siliconoxide in a recovery chamber.

[0006] According to one aspect of the invention, there is provided amethod for continuously preparing a silicon oxide powder, comprising thesteps of feeding a raw material powder mixture containing silicondioxide powder into a reaction furnace; heating the mixture in thefurnace in an inert gas or in vacuum to a temperature of 1,100 to 1,600°C. to produce a silicon oxide gas; introducing the silicon oxide gasinto a cooling chamber through a transfer conduit which is maintained ata temperature of from higher than 1,000° C. to 1,300° C., therebycausing silicon oxide to deposit on a surface of a substrate which isdisposed and cooled in the cooling chamber; and continuously recoveringthe silicon oxide deposit.

[0007] According to another aspect of the invention, there is providedan apparatus for continuously preparing a silicon oxide powder,comprising a charge feed means for feeding a raw material powder mixturecontaining silicon dioxide powder to a reaction chamber; the reactionchamber where the raw material powder mixture is reacted to produce asilicon oxide gas; a transfer line for transferring the silicon oxidegas from the reaction chamber to a deposition chamber; the depositionchamber in which a substrate is disposed and cooled so that siliconoxide deposits on a surface of the cooled substrate; and a recoverymeans for recovering the silicon oxide deposit on the substrate.

BRIEF DESCRIPTION OF THE DRAWING

[0008] The only FIGURE, FIG. 1 is a schematic illustration of anapparatus for continuously producing silicon oxide powder according tothe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0009] In the method for the continuous production of silicon oxidepowder according to the invention, the raw material used is typically amixture of a silicon dioxide powder and a reducing powder therefor.Exemplary reducing powders are metal silicon compounds andcarbon-containing powders. Of these, metal silicon powder is preferablyused since it is effective for enhancing reactivity and increasing apercent yield.

[0010] The raw material powder mixture is fed to a reaction furnace orchamber where it is heated and held at a temperature of 1,100 to 1,600°C., preferably 1,200 to 1,500° C., to produce a silicon oxide gas.Temperatures below 1,100° C. may retard the progress of reaction,resulting in a reduced productivity. Temperatures above 1,600° C. maycause the raw material powder mixture to melt, rather adversely affectreactivity, and impose a difficult choice of the furnace material.

[0011] The atmosphere in the furnace is an inert gas or vacuum. Reactionin vacuum is desired from thermodynamic considerations because thevacuum atmosphere provides higher reactivity and allows for reaction atlower temperature.

[0012] To the reaction chamber, the raw material powder mixture is fedat suitable intervals or continuously by a charge feed mechanism orfeeder, so that reaction may be continuously effected.

[0013] The silicon oxide gas produced in the reaction chamber iscontinuously fed to a deposition chamber through a transfer line.

[0014] The transfer line is heated and held at a temperature of fromhigher than 1,000° C. to 1,300° C., and preferably 1,100 to 1,200° C. Ifthe temperature of the transfer line is 1,000° C. or lower, the siliconoxide vapor will deposit and stick on the inner wall of the transferline, causing troubles to the operation and precluding stable continuousoperation. Heating to a temperature above 1,300° C. achieves no furthereffect and requires an increased electric power cost.

[0015] Disposed in the deposition chamber is a substrate having asurface. The substrate is cooled. When the silicon oxide gas isintroduced into the deposition chamber and brought into contact with thecooled substrate so that the gas is cooled thereby, silicon oxide powderdeposits on the substrate surface. The substrate is cooled for thepurpose of producing amorphous silicon oxide. If the substrate is notcooled, the once deposited silicon oxide will undergo disproportionationreaction to separate into silicon dioxide and metallic silicon, orcrystalline metal silicon is partially contained. The type of coolant isnot critical although a choice may be made among liquids such as waterand heat transfer media and gases such as air and nitrogen, depending ona particular purpose. Also the type of substrate is not critical, andhigh-melting metals such as stainless steel, molybdenum and tungsten arepreferably used for ease of working. Preferably the substrate is cooledto a temperature of 200 to 500° C., and especially 300 to 400° C.

[0016] The silicon oxide powder deposited on the substrate is recoveredby suitable means such as a scraper.

[0017] Referring to FIG. 1, there is illustrated one exemplary apparatuswhich can be used in practicing the above method. The apparatusgenerally includes a charge feed mechanism 6, a reaction furnace 1, atransfer line 10, a deposition tank 11, and a recovery tank 18 connectedin fluid communication. The reaction furnace 1 defines therein areaction chamber 2 for receiving a raw material powder mixture 3. Aheater 4 is disposed around the reactor furnace 1 so that the reactionchamber 2 may be heated at a temperature of 1,100 to 1,600° C. byconducting electricity to the heater 4. The reactor furnace 1 is furthercovered with a thermal insulator 5.

[0018] The charge feed mechanism 6 includes a hopper 7, a feeder 8, anda feed tube 9. The feeder 8 operates such that the raw material powdermixture is fed from the hopper 7 to the feeder 8 and then to thereaction chamber 2 through the feed tube 9. The feed operation can beeffected in an intermittent or continuous manner while detecting thepressure P in the reaction furnace or chamber and estimating the amountof the raw material in the reaction chamber.

[0019] The deposition tank 11 is connected to the reaction furnace 1through the transfer conduit or line 10. A. heater is mounted on thetransfer conduit 10 so as to maintain the conduit interior at atemperature from higher than 1,000° C. to 1,300° C. The deposition tank11 defines therein a deposition chamber 12 where a substrate 13 isdisposed horizontally. The substrate 13 is provided with a coolantcircuit (not shown) which communicates with a coolant inlet tube 14 anda coolant outlet tube 15. As coolant flows through the coolant circuit,the substrate 13 is cooled to a predetermined temperature. The transferconduit 10 extends transverse to one major surface of the substrate 13so as to ensure the silicon oxide gas strikes and contacts the substrate13 whereby silicon oxide powder deposits on the substrate 13. A siliconoxide powder recovery mechanism in the form of a scraper 16 isassociated with the substrate 13 for scraping and recovering siliconoxide powder deposit on the substrate 13.

[0020] The recovery tank 18 is connected to the deposition tank 11through a discharge conduit 17. The silicon oxide powder which depositson the substrate 13 in the deposition chamber 12 and is scraped andcollected by the scraper 16 falls through the discharge conduit 17 intothe recovery tank 18. In this way, the silicon oxide powder isrecovered. It is noted that vacuum pumps 19, 20 and 21 are connected tothe hopper 7, the deposition tank 11, and the recovery tank 18,respectively.

[0021] The apparatus illustrated above enables continuous and stableproduction of amorphous silicon oxide powder.

[0022] The silicon oxide powder produced by the above method andapparatus generally has a BET specific surface area of 0.5 to 300 m²/g,especially 5 to 100 m²/g and a purity of at least 99.9%, especially atleast 99.95%. The silicon oxide powder is suitable for use in vapordeposition on package film and as lithium ion secondary battery negativeelectrode active material.

EXAMPLE

[0023] Examples of the invention are given below by way of illustrationand not by way of limitation.

Example

[0024] A silicon oxide powder was produced using the continuousproduction apparatus illustrated in FIG. 1. The raw material was apowder mixture obtained by mixing equimolar amounts of silicon dioxidepowder having a BET specific surface area of 200 m²/g and metallicsilicon powder having BET specific surface area of 3 m²/g in anagitator. The reaction furnace 1 defining the reaction chamber 2 with avolume of 0.5 m³ was charged with 20 kg of the powder mixture. Thevacuum pump was actuated to evacuate the chamber 2 to a vacuum below 0.1Torr. The heater 4 was energized to heat and hold the chamber 2 at atemperature of 1,300° C. The transfer conduit 10 was heated and held ata temperature of 1,100° C. Water was fed into the coolant inlet tube 14to cool the stainless steel substrate 13. Next, the feeder 8 wasoperated to continuously feed the raw material powder mixture at a rateof 2 kg/hr into the reaction chamber to effect continuous reaction. Assilicon oxide deposited on the substrate 13, the deposit wascontinuously scraped by the scraper 15 and recovered in the recoverychamber 18. The operation was continued for 120 hours whereupon siliconoxide powder was recovered at a rate of 1.6 kg/hr and in a yield of 80%.The silicon oxide powder obtained was an amorphous powder having a BETspecific surface area of 8 m²/g and a purity of at least 99.9%. Afterthe completion of operation, the interior of the apparatus wasinspected, finding that the respective units remained intact.

Comparative Example 1

[0025] Silicon oxide was continuously produced under the same conditionsas in Example except that the transfer conduit 10 was set at 1,000° C.The silicon oxide powder obtained was an amorphous powder having a BETspecific surface area of 8 m²/g and a purity of at least 99.9%. After 25hours from the start of operation, the transfer conduit 10 was cloggedwith the silicon oxide deposit, and the operation could no longer becontinued.

Comparative Example 2

[0026] Silicon oxide was continuously produced under the same conditionsas in Example except that the substrate 13 was not cooled. Uponinspection of the interior of the apparatus after the completion ofoperation, no significant problem was found. The silicon oxide powderobtained was found to contain crystalline metal silicon and was a lowpurity powder having a BET specific surface area of 4 m²/g and a purityof at least 92%.

[0027] The method and apparatus of the invention is capable ofcontinuous and stable production of amorphous silicon oxide powder at ahigh purity and as a consequence, ensures delivery of inexpensivesilicon oxide to the market.

[0028] Japanese Patent Application No. 2000-027582 is incorporatedherein by reference.

[0029] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

Claims:
 1. A method for continuously preparing a silicon oxide powder,comprising the steps of: feeding a raw material powder mixturecontaining silicon dioxide powder into a reaction furnace, heating themixture in the furnace in an inert gas or in vacuum to a temperature of1,100 to 1,600° C. to produce a silicon oxide gas, introducing thesilicon oxide gas into a cooling chamber through a transfer conduitwhich is maintained at a temperature of from higher than 1,000° C. to1,300° C., thereby causing silicon oxide to deposit on a surface of asubstrate which is disposed and cooled in the cooling chamber, andcontinuously recovering the silicon oxide deposit.
 2. The method ofclaim 1 wherein the raw material powder mixture is a mixture comprisedof a silicon dioxide powder and a metal silicon powder.
 3. An apparatusfor continuously preparing a silicon oxide powder, comprising a chargefeed means for feeding a raw material powder mixture containing silicondioxide powder to a reaction chamber, the reaction chamber where the rawmaterial powder mixture is reacted to produce a silicon oxide gas, atransfer line for transferring the silicon oxide gas from the reactionchamber to a deposition chamber, the deposition chamber in which asubstrate is disposed and cooled so that silicon oxide deposits on asurface of the cooled substrate, and a recovery means for recovering thesilicon oxide deposit on the substrate.